Template based synthesis of mesoporous silica material and its application in removal of fluorescent dyes.

Dye encapsulated uniform mesoporous silica particles have been synthesized using the surfactant assisted sol gel method. The release profile of the dye in different solvents (water and ethanol) has been studied. It is observed that the release of dye is controlled by the type of solvent chosen. When dispersed in ethanol the concentration of dye molecules released is much higher than what we observe when the release is carried out under aqueous conditions. The initial increase in the fluorescence intensity in both ethanol and water is a contribution from the initial burst of dye molecules present on the outer surface. Apart from the in-situ encapsulation of the fluorescent dye, mesoporous silica particles were also used as nanocontainers for storing dye molecules. The post synthesis adsorption of the dye on mesoporous silica was also carried out and the effective concentration of the dye molecule was found to decrease with increase in time. This study shows that mesoporous silica particles can be used for the in-situ encapsulation of organic molecules and also as a host for dye molecules by employing the simple post adsorption technique.

Structural characterization and antimicrobial properties of silver nanoparticles prepared by inverse microemulsion method.

Silver nanoparticles have been synthesized in the inverse microemulsions formed using three different surfactants viz., cetyl-trimethyl ammonium bromide (CTAB), Tergitol and Triton X-100. We have done a systematic study of the effect of the surfactants on the particle size and properties of the silver nanoparticles. Microscopic studies show the formation of spheres, cubes and discs shaped silver nanostructures with the size in the range from 8 to 40 nm. Surface plasmon resonance (SPR) peak was observed around 400 nm and 500 nm. In addition to SPR some extra peaks have also been observed due to the formation of silver metal clusters. The surface area increases from 3.45 to 15.06 m(2)/g with decreasing the size of silver nanoparticles (40-8 nm). To investigate the antimicrobial activity of silver nanoparticles, the nanoparticles were tested against the yeast, Candida albicans and the bacterium, E. coli. The results suggest very good antimicrobial activity of the silver nanoparticles against the test microbes. The mode of action of the antimicrobial activity was also proposed.

Reverse micellar based synthesis of ultrafine MgO nanoparticles (8-10 nm): characterization and catalytic properties.

Anisotropic nanostructures of magnesium oxalate dihydrate were synthesized using cationic surfactant based microemulsion method. The cationic surfactant plays an important role in forming the anisotropic structures. The oxalate nanostructures acts as an excellent precursor for the synthesis of fine magnesium oxide nanoparticles (~10 nm). Both the precursor and the oxide were characterized by using PXRD, IR, surface area and HRTEM. The surface area of these surfactant free oxide nanoparticles was found to be 108 m(2)/g. The catalytic activity of this basic oxide was examined for the Claisen-Schmidt condensation reaction and was found to be comparable to the best reported for the conventionally prepared MgO. Chalcone formation was found to increase with time as observed using gas chromatography-mass spectrometry (GC-MS). The reusability of the catalyst was checked by using the same catalyst twice which showed a reduced percentage (50% compared to first cycle) conversion.

Silica mesostructures: control of pore size and surface area using a surfactant-templated hydrothermal process.

The cooperative self-assembly of the silica precursor, tetraethyl ortho silicate (TEOS), with the surfactant molecule followed by the basic hydrolysis led to the formation of mesoporous silica with varying pore sizes. The pores are formed by the removal of the intermediate assemblies of the charged surfactant molecules. In the absence of formation of such assemblies of surfactants (example in the case of nonionic surfactants), the resulting mesostructures have very small pores, giving low surface area mesostructures. This study outlines the precise control of pore size in a wide size distribution (3.4-22 nm) by the systematic variation of the surfactant. The addition of polyethylene glycol (in situ) while carrying out the hydrolysis of TEOS results in the formation of large-sized cavities (∼40 nm). Uniform spherical particles with pores (different from the cavities) as large as 22 nm and surface areas of ∼1100 m(2)/g have been obtained by the combined effect of the hydrothermal conditions on the cetyl trimethyl ammonium bromide-templated synthesis.

Microemulsion-based synthesis of nanocrystalline materials.

Microemulsion-based synthesis is found to be a versatile route to synthesize a variety of nanomaterials. The manipulation of various components involved in the formation of a microemulsion enables one to synthesize nanomaterials with varied size and shape. In this tutorial review several aspects of microemulsion based synthesis of nanocrystalline materials have been discussed which would be of interest to a cross-section of researchers working on colloids, physical chemistry, nanoscience and materials chemistry. The review focuses on the recent developments in the above area with current understanding on the various factors that control the structure and dynamics of microemulsions which can be effectively used to manipulate the size and shape of nanocrystalline materials.

Self-assembly of copper succinate nanoparticles to form anisotropic mesostructures.

Uniform cylindrical rods of copper succinate dihydrate of several microns in length and 200 nm in diameter were obtained by the reverse micellar (microemulsion) method at room temperature using CTAB as the surfactant. The rod-like structures are formed by an ordered assembly of spherical particles of 4-5 nm, which is facilitated by water molecules. The copper succinate particles, in the absence of the microemulsion or surfactant, show only spherical geometry, while in the presence of the surfactant, thicker rods (compared to as obtained by reverse micellar method) of varying length were obtained. The formation of the rod-like structure is driven by the permanent dipole moment of the succinate ion, which leads to the oriented attachment of the nanoparticles in the presence of the surfactant. A new phase (anhydrous copper succinate) is obtained upon heating the dihydrate at 75 degrees C, which shows branched and corrugated rods assembled from a random arrangement of nanoparticles. The water molecules appear to control the morphology of the rods giving smooth rods (ordered arrangement of nanoparticles) for the dihydrate while branched or disrupted rods with random arrangement of nanoparticles are obtained for the anhydrous phase. The chain length of the dicarboxylic acid (ligand) appears to have a role in controlling the aspect ratio of these anisotropic mesostructures. The ability to generate suitable conditions for self assembly into ordered nanostructures and to control the anisotropy would lead us towards a proper design of nanodevices.